An artificial leg or prosthesis for a person who has a below-the-knee amputation and has tissues which are sensitive to the pressures and friction associated with the use of a prosthesis presents a significant problem if reasonably full use of the knee is to preserved. As is the case with conventional prosthesis, these artificial limbs are usually fitted to the stump of the leg below the knee and strapped to the leg above the knee so that use of the knee for walking may be preserved. However, because this limb is fitted to the stump and the stump and limb are not one in the same, significant stresses during movement of the limb will tend to irritate the stump in the area where it contacts the prosthesis. Therefore, the need for a lightweight prosthesis is apparent particularly when fitting very weak geriatric patients with this type of prosthesis.
Numerous attempts have been made to develop a prosthesis which is both lightweight and structurally sound in order to perform functions similar to that of the natural limb. Some of these attempts have included an articulated toe and ankle section in an attempt to imitate nature by duplicating the functions of the natural foot. The importance of the cosmetic aspects of such an articulated limb are not to be denied, however, the simulation of these joints as well as that of the weight of a natural leg results in a limb which is difficult to maneuver due to an extreme excess of weight. The prosthesis is not a natural limb and, as mentioned above, cannot function in all respects as a natural integral limb.
In one attempt to overcome the shortcomings associated with the use of a below-the-knee prosthesis is set forth in U.S. Pat. No. 3,909,855 issued to Barredo. This below-the-knee prosthesis is a hollow rigid lightweight non-articulated prosthesis having a foreshortened foot which is fitted to the stump of a below-the-knee amputee. This prosthesis is of a unitary hollow shell formed of fiber glass and includes a foreshortened foot. This foreshortened foot portion is shortened by a length approximately equal to the toes of a natural foot and allows the prosthesis wearer to walk in a manner somewhat like that of a natural walk. However, the foreshortened foot exhibits no shock absorption characteristics and therefore any shock to the foot portion of this prosthesis will be absorbed completely by the stump of the wearer. Moreover, the foreshortened foot portion is not cosmetically pleasing to either the wearer or others.
A currently favored simplification of the articulated toe and ankle prosthesis is that of a prosthesis having a solid ankle portion and cushioned toe, heel and sole attached thereto, commonly known as the SACH foot design which is fixed to the bottom portion of the prosthesis.
In previously known SACH-type prosthesis, the socket portion of the prosthesis was formed in a conventional manner. The socket may then be adhered to a copolymer prosthesis having a solid ankle portion. Initially, the copolymer completely encompassed the solid ankle and consequently the cushioned or resilient heel was adhered directly to the bottom of the prosthesis, however, a reliable bond between the resilient heel and the copolymer prosthesis was not achievable due to the nature of the copolymer.
In order to overcome the above-mentioned problem, the bottom of the solid ankle portion was left exposed; i.e., with no copolymer material extending thereover and consequently a strong adhesion could be formed between the foam material of the solid ankle portion and the resilient material of the heel portion. However, because a majority of the foam is removed from within the prosthesis in order to significantly reduce the weight of the prosthesis, during use the keel would detach from the copolymer material of the prosthesis and pull out of the prosthesis resulting in a separation between the resilient heel and the shin portion of the prosthesis thus resulting in a lack of confidence in the structural integrity of the prosthesis. Additionally, because the prosthesis was susceptible to such structural damage, use of the prosthesis was limited to inactive below-the-knee amputees.
Clearly, there is a pressing need for a lightweight and structurally sound prosthesis that may be worn by both nonactive as well as active amputees who can wear the prosthesis while performing any activity without fear of any catastrophic failures.